Evolutionary history and ecological adaptations of ammonia oxidizing Thaumarchaeota

Ammonia oxidizing archaea (AOA), a clade of the Thaumarchaeota phylum, diversified in a variety of marine and terrestrial environments. Due to their abundance, AOA are deemed major players in the global cycle of nitrogen. They also produce greenhouse gasses. Despite their ecological importance, the nature and origin of ammonia oxidizing metabolism and the reasons for the ecological success of AOA are still unknown. This project aims at performing the first comprehensive evolutionary and comparative genomic analysis of Thaumarchaeota to identify crucial metabolic and genomic features. Metagenomic data produced in the laboratory will give access to genomes of crucial taxa for this project. These genomes will be completed, and analysed together with AOA genomes available in the databanks with a sophisticated model of genome evolution to reconstruct the species tree of Thaumarchaeota and the events (gene duplications, transfers and losses) that occurred along their evolution. The genome of the AOA's ancestor will be inferred, and the minimal gene set required for ammonia oxidation identified. The sets of evolutionary events and the ancestral genome will be linked to metabolic and ecological transitions to obtain the scenario of ammonia oxidation emergence and of the adaptation of AOA to various environments, thus addressing key questions in the fields of ecology, evolution, and archaea biology.

Simulation models predict that the oxygen content of the global ocean will decrease by 25% until the end of the century due to an increased stratification of the oceanic surface waters and a rise in temperature. This loss in oxygen will inevitably lead to an expansion of hypoxic and anoxic areas in the global ocean with major consequences for the oceanic carbon and nitrogen cycling. In this proposal, we assess the functional diversity of chemolithoautotrophic prokaryotic communities in two contrasting marine environments, the deep-water masses of the North Atlantic along a latitudinal gradient and around the redoxcline in the central Baltic Sea. Both environments have been shown previously to harbor highly active chemolithoautotrophic prokaryotic communities with dark carbon dioxide fixation rates approaching surface water phytoplankton activity. Specific focus is put on the functional diversity of prokaryotes in the carbon and nitrogen cycling in both systems, including the sulfur cycle in the central Baltic. Biogeochemical rate measurements are tightly linked to functional gene analyses using among other approaches metagenomics and metatranscriptomics. Information obtained from these analyses will guide the development of primers for QPCR to determine the abundance of genes indicative for geochemically relevant processes in the water column of the two systems. Incubation experiments using stable and radio-isotopes in combination with molecular techniques such as SIP-RNA analyses, single-cell analyses using Raman-FISH, NanoSIMS and MICRO-FISH will allow insights into the dynamics of the functional diversity of chemolithotrophic microbial communities in suboxic and anoxic marine planktonic systems. Field studies will be complemented by laboratory model systems with isolated key players in order to understand the adaptive capacity and performance of chemolithoautotrophs in response to different environmental conditions. The combination of these approaches will provide the base for a significant advancement in our understanding of planktonic chemolithoautotrophy in the dark ocean.

Long Term Carbon Storage in Cryoturbated Arctic Soils - CryoCarb

The overarching goal of CryoCARB is to advance organic carbon estimates for cryoturbated soils, focusing on the Eurasian Arctic and to understand the vulnerability of these carbon stocks in a future climate. Our vision is that one can build on this knowledge to improve existing models to better predict the responses of cryoturbated soils to future climate conditions. The constraints to our understanding of carbon dynamics in cryogenic soils are currently manifold. First, due to cryoturbation, organic matter is unevenly distributed within the soil, making SOC estimation very difficult. There is evidence that the North American arctic carbon stock is bigger than previously thought, also because of underestimation of carbon stored in distorted, broken and warped horizons. Second, most studies dealing with SOC in arctic soils fail to account for carbon stored in the upper permafrost, although the latter is directly under threat in a rapidly warming Arctic. Thawing of the upper permafrost will also mobilize old, geogenic C, which is rarely addressed. Third, the mechanisms of carbon stabilization are largely unknown thus hampering the prediction of climate-C02 feedbacks. Knowledge of the chemical composition of organic matter and the processes on how carbon is stabilized is necessary to predict the magnitude and the time-scale at which SOC will get remobilized from thawing permafrost under climate change.

A Silicon cell model for the central carbohydrate metabolism of the archaeon Sulfolobus solfataricus under temperature variation - Sysmo

Temperature changes are not only most difficult to deal with for organisms, it is also unclear how biological networks can withstand and respond to such changes. Even slight differences between the rates of individual reactions in metabolic pathways should cause rapid accumulation or depletion of intermediates with various deleterious effects. With a change in temperature, the rates of individual reactions in metabolic pathways must therefore change by precisely the same extent. Organisms could adapt by (i) having identical temperature coefficients of the enzymes, (ii) metabolic regulation, (iii) adjusting Vmax-s (e.g. through enzyme phosphorylation), (iv) adjusting translation or protein stability, (v) adjusting transcription or mRNA stability, (vi) rerouting the metabolic flow, (vii)formation of compatible solutes, (viii) export of overflow metabolites or (ix) going into dormancy. We hypothesize that several of theses mechanisms contribute to different extents and will try to quantify each of these adaptations in a systems biology approach. As the issue should be most acute for thermophiles, we will perform these studies with a thermophilic archaeon.The archaeal model organism of choice for this systems biology approach is Sulfolobus solfataricus, a thermoacidophilic Crenarchaeon that grows at around 80°C and pH 3 [2]. S. solfataricus uses an unusual branched Entner-Doudoroff (ED) pathway for glucose catabolism [3]. Life at high temperature requires a very efficient adaptation to temperature changes, which is most difficult to deal with for organisms and it is unclear how biological networks can withstand and respond to such changes. In this sysmo project,10 partner laboratories will study the central carbohydrate metabolism (CCM), i.e. the branched ED pathway of S. solfataricus and its regulation under temperature variation by the integration of genomic, transcriptomic, proteomic, metabolomic, kinetic and biochemical information. The long term goal of the project is to build a sufficiently precise replica for this part of the living cell (“a Silicon Cell”) to enable computation of life, particular its robustness to changes in temperature, at the system level.

Meta-transcriptomics to study the function and structure of complex microbial communities

We are interested in the characterisation of complex microbial communities with cultivation-independent molecular genomic approaches to disclose the ecological function of uncultured archaea and bacteria. Meta-genomic technologies have been used for many years for this purpose and as a logical next step we have recently established meta-transcriptomic approaches in our laboratory.transcriptomics offers the opportunity to reach beyond the community’s genomic potential as assessed in DNA-based methods, towards its in situ activity. In addition, the analysis of the RNA pool of a community links its taxonomic structure and function, as it is naturally enriched not only in functionally but also taxonomically relevant molecules, i.e. mRNA and rRNA, respectively. In addition rRNA can be used for PCR-independent community profiling of all three domains of life.

Sponges as nutrient sources and sinks in the marine ecosystem

Sponges are major constitutes of coral reef and deep sea communities. They excrete high amounts of ammonium and, due to the activity of associated microorganisms, nitrite and nitrate; these are essential nutrients, and sponges are thus considered as important nutrient sources in the marine ecosystem. A team of researchers from CGB, the Max Planck Institute for Marine Microbiology in Bremen (Germany) and the University of Vienna (Austria) have recently discovered an alternative role of sponges: under certain conditions, sponges transform these nutrients to elemental nitrogen and thereby remove them from the system; these sponges function as nutrient sinks in the ocean.

Although prokaryotic in cell structure, Archaea have been recognized as a third primary evolutionary lineage, being as distinct from true Bacteria as they are from Eukaryotes. Phylogenetic and genomic analyses indicate that Archaea and Eucarya are probably sister groups that share a number of homologous factors involved in replication, transcription and translation. Therefore, the study of information processing in the simpler systems of the Archaea is often directly relevant for understanding cellular evolution and the more complex interactions that occur in the eucaryal nucleus. Most cultivated archaea thrive under extreme environmental conditions, such as temperatures between 70 - 113 °C, low pH or high salt concentrations. However, with molecular ecological methods, specific lineages of archaea have also been detected in common place environments, as for example soils and the marine plankton. Their high abundance indicates, that these archaea should be of global ecological significance. However, their phenotypic and physiological properties are still largely unknown. Our research interests involve: - the study of stress-induced transcriptional regulation in the hyperthermophilic archaeon Sulfolobus solfataricus and its virus SSV1 to get insights into global regulatory networks and into regulatory factors interacting with the basic (eucaryotic-like) transcription machinery in hyperthermophilic archaea - the characterization of as yet uncultivated microorganisms, in particular of archaea, by metagenomic and novel postgenomic techniques.